Hierarchical sorting of linked objects in virtual three-dimensional space

ABSTRACT

An information processing apparatus displays a plurality of linked objects in a virtual three-dimensional space in accordance with field-of-view data. The information processing apparatus includes control means for generating images of the objects in accordance with the object data and in accordance with the field of view and rendering the generated images onto a two-dimensional frame. The control means hierarchically sorts the objects in accordance with link data which indicates links between the objects. The control means renders the image of one object and the image of another object to which the one object is linked, wherein the image of the other object is rendered before the start of or after the end of rendering the one object or between the start and the end of rendering.

This application is a continuing application, filed under 35 U.S.C. §111(a), of International Application PCT/JP01/09052, filed Oct. 15, 2001.

FIELD OF INVENTION

The present invention generally relates to rendering images ofthree-dimensional objects, and more particularly to hierarchicallysorting a plurality of linked objects in a virtual three-dimensionalspace for efficiently rendering images of the objects.

BACKGROUND OF THE INVENTION

Today, a shopping mall is provided on a Web page on the Internet. Such ashopping mall may be a virtual three-dimensional world. A number ofthree-dimensional commodity objects are disposed within a virtual shopobject in the shopping mall. In accordance with a virtualthree-dimensional image displaying program, a server machine or a clientmachine may generate images in the virtual three-dimensional shoppingmall for displaying. One of the objects within the virtual shopping mallmay be linked to another one of the objects by means of a URL.

A conventional virtual three-dimensional image displaying program isoperative to dispose objects in a virtual three-dimensional space inaccordance with sets of object data representative of three-dimensionalshapes and positions of the objects, and to project the objects on atwo-dimensional plane in accordance with a field of view of a user inthe space to thereby generate corresponding two-dimensional images. Whentwo objects partially overlap with each other as viewed from the user'sviewpoint, the images of these objects must be generated so that theoverlapping portion of one object which is deeper or farther from theviewpoint hides behind the other object which is shallower or closer tothe viewpoint. Meanwhile, when there is disposed a semi-transparentobject, the images of the objects must be generated so that the objectsbehind the semi-transparent object can be seen through thesemi-transparent object.

The Z buffer algorithm is typically used in order to properly processrelative overlapping of objects as viewed from the viewpoint. Inaccordance with this algorithm, for rendering the images of objects ontoa two-dimensional frame buffer memory, the objects are separated intoelemental polygons, and Z-values representative of positions of aplurality of polygons of the objects relative to the viewpoint arestored in a so-called Z buffer. For rendering pixels of two or moreobject polygons at the same pixel locations onto the two-dimensionalframe buffer memory, in accordance with the algorithm, the Z-values ofthe object polygons are compared with each other and only the pixels ofone of the object polygons that is closest to the viewpoint areultimately stored at the locations. For rendering an image of asemi-transparent object, a so-called alfa blending method is used torender, onto the frame buffer memory, values representative of a colorof the pixels of the semi-transparent object blended with colors of thepixels of other object polygons disposed behind the semi-transparentobject in accordance with the degree of the transparency of thesemi-transparent object.

According to the Z buffer algorithm and the alfa blending method, forrendering the image of the semi-transparent object, the objects must berendered in order of the distance from farther object polygons to closerobject polygons relative to the viewpoint. For this purpose, before therendering, a so-called Z sorting method is used to first determine thedistances of all of the displayed object polygons from the viewpoint andthen sort the object polygons in accordance with the distances.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, an informationprocessing apparatus displays a plurality of linked objects in a virtualthree-dimensional space in accordance with field-of-view data. Theinformation processing apparatus includes control means for generatingimages of the objects in accordance with the object data and inaccordance with the field of view and rendering the generated imagesonto a two-dimensional frame. The control means hierarchically sorts theobjects in accordance with link data which indicates links between theobjects, for the rendering.

In an embodiment of the invention, the control means may render theimages and/or partial images of the objects in order determined by thehierarchical sorting. The control means may render images and/or partialimages of objects of a group of one object and one or more other objectsto which the one object is linked, in order of the distance from theviewpoint.

In accordance with another aspect of the invention, an informationprocessing apparatus includes control means for generating images of theobjects in accordance with the object data stored in the memory andrendering the generated images onto a two-dimensional frame. The controlmeans renders the image of one object and the image of another object towhich the one object is linked. The image of the other object isrendered before the start of or after the end of rendering the oneobject or between the start and the end of rendering.

In an embodiment of the invention, the control means may render theimage or partial images of the one object and the image of the otherobject in accordance with the distance from the viewpoint.

In accordance with a further aspect of the invention, an object dataprocessing method is for displaying a plurality of linked objects in avirtual three-dimensional space in accordance with field-of-view data.The method includes the step of hierarchically sorting the objects inaccordance with link data which indicates links between the objects, thestep of generating images of the objects in accordance with the objectdata and in accordance with the field of view, and the step of renderingthe generated images onto a two-dimensional frame in order determined bythe hierarchical sorting.

In accordance with a still further aspect of the invention, an objectdata processing method includes the step of generating images of theobjects in accordance with the object data, and the step of renderingthe generated images onto a two-dimensional frame. The step of renderingincludes rendering the image of one object and the image of anotherobject to which the one object is linked. The image of the other objectis rendered before the start of or after the end of rendering the oneobject or between the start and the end of rendering.

In an embodiment of the invention, the methods above may be implementedin the form of programs which can be executed by an informationprocessing apparatus.

According to the invention, a plurality of linked three-dimensionalobjects can be sorted in an advantageous manner, and images of aplurality of linked three-dimensional objects can be efficientlyrendered. According to the invention, not all polygon surfaces arerequired to be sorted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a configuration of an information processing apparatus inaccordance with an embodiment of the present invention;

FIG. 2 shows the structure of an object data set of an object;

FIG. 3 shows the hierarchy of a plurality of linked objects which arerepresented by a plurality of respective linked object data sets;

FIG. 4 is a schematic flow chart for generating and rendering images ofthe objects that is executed by the controller in accordance with athree-dimensional Web browser program;

FIG. 5 shows a schematic flow chart for rendering the images of theobjects in accordance with the invention;

FIG. 6 shows an example of the geometrical relationships between a fieldof view of a user and objects;

FIGS. 7A to 7C show an example of display screens of object imagesduring the zooming-in operation, in accordance with movement of theviewpoint;

FIGS. 8A to 8E show an example of a process for rendering images of theplurality of objects in accordance with the invention;

FIG. 9A shows a displayed image in which the object in FIG. 8E issemi-transparent; and

FIG. 9B shows a displayed image in which the objects in FIG. 9A aresemi-transparent.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the conventional algorithm above, when a number of objects arearranged in a virtual three-dimensional space, a long time and a largememory resource are required to sort object polygons thereof. Thus thesorting may not be desirable for real-time displaying ofthree-dimensional images.

The inventors have recognized that hierarchical sorting of a pluralityof linked three-dimensional objects can provide efficient rendering ofimages of the objects.

An object of the present invention is to efficiently render images of aplurality of three-dimensional objects.

Another object of the invention is to sort a plurality of linkedthree-dimensional objects in an advantageous manner to render images ofthe objects.

FIG. 1 shows the configuration of an information processing apparatus100 in accordance with an embodiment of the present invention. Theinformation processing apparatus 100 includes an input device 101, acontroller or processor 103, an object data manager 104, a displaydevice 106, an information storage device 107, a program memory 112, anobject data memory 113, and a network interface 127 connected to a Webserver 200 via a network 50.

The information processing apparatus 100 displays, on the display device106, a plurality of linked three-dimensional objects which are arrangedin a virtual three-dimensional space.

A three-dimensional object is formed of one or more polygon surfaces,each polygon surface typically having an outer side surface and an innerside surface. A curved surface may be expressed typically by a pluralityof polygon surfaces.

A three-dimensional object is formed by one or more polygons, andvisually represents, in a virtual three-dimensional space, any item ofinformation content handled as a unit, such as a single text document, adocument containing text and graphics, an image, a stream of motionpictures, a three-dimensional image made up of a plurality of parts, anaudio stream or the like.

The network 50 typically consists of the Internet, a local area network(LAN), a telephone network including a mobile communication network, acable, TV network, a power line carrier communication network, a fiberoptic network and/or the like.

The controller 103 includes a CPU, a RAM 122 and a ROM. The controller103 operates in accordance with programs stored in the program memory112, such as a browser program to implement the browser function. Thecontroller 103 may be a processor, the browser function of which isimplemented in the form of an integrated circuit. The object datamanager 104 may be implemented as a processor which operates inaccordance with a program for object data management, or as a processorwhich has a function of the management implemented in the form of anintegrated circuit.

When content data is required for displaying an object, the controller103 captures the content data from the Web server 200 via the networkinterface 127 over the network 50 and provides the captured content datato the object data manager 104. The controller 103 may capture therequired content data from the information storage device 107. Theobject data manager 104 stores the captured object data set in theobject data memory 113 and manages the object data set.

The input device 101 provides, to the controller 103, input data such asa URL and field-of-view data in response to operation by a user. Uponreceipt of the field-of-view data, the controller 103 holds thefield-of-view data, and updates the field-of-view data in accordancewith user's input data.

For generating a displayed image, the controller 103, in accordance withthe object data set stored in the object data memory 113, generates inreal time an object image which changes as the field-of-view moves, anddisplays the object image on the display device 106.

FIG. 2 shows the structure of an object data set 30 of an object. Theobject data set 30 contains at least data 31 representative of athree-dimensional shape of the object. When a current object having thedata set 30 is linked to another subsequent object, the object data set30 contains a list of link data 40. The other object to be linked to hasa position which is associated with the current object. The list of linkdata 40 contains one or more link data sets 37. The link data set 37contains an identification 38 of the other object which indicates a linkto the other object and a coordinate transformation matrix 39 fortransforming the coordinates of the other object into the coordinates ofthe current object. The object data set 30 may be linked to a pluralityof objects. Thus, the object data set 30 may contain a plurality of linkdata sets as shown in the figure.

FIG. 3 shows the hierarchy of a plurality of linked objects which arerepresented by a plurality of respective linked object data sets. Theseobjects are sorted in accordance with the hierarchy, for rendering.

In FIG. 3, an object data set 301 of a starting object includes threelink data sets 211, 212 and 213 which contain respective identificationsof the other objects to be linked to. The starting object is linked tothe other three objects which have respective object data sets 311, 312and 313. The object data set 311 has three link data sets 221, 222 and223. The object having the object data set 311 is linked to threeobjects which have respective object data sets 321, 322 and 323. Theobject having the object data set 312 is similarly linked to an objectwhich has an object data set 324. The object having the object data set313 is linked to two objects which have respective object data sets 325and 326. The objects having the object data sets 321, 323, 324 and 325are linked to further objects. The objects having the object data sets322 and 326 are not linked to further objects.

As described later in greater detail, it is possible to efficientlyrender the images of the plurality of linked objects onto a frame memoryarea of the RAM 122 in accordance with the hierarchically-layeredobjects.

FIG. 4 is a schematic flow chart for generating and rendering the imagesof the objects that is executed by the controller 103 in accordance withthe three-dimensional Web browser program.

The controller 103 captures the object data set of an initial object andthe object data sets of other subsequent objects which are directly orindirectly linked to the initial object via the network 50 or from theinformation storage device 107 in accordance with a URL entered by auser, and stores the captured object data sets in the object data memory113 via the object data manager 104. After that, the controller 103generates and renders the images of the objects in accordance with theflow chart of FIG. 4.

At Step 402, the controller 103 acquires data of a viewpoint and a fieldof view that is entered through the input device 101, for example amouse, and moves the viewpoint and the field of view relative to thevirtual three-dimensional space in accordance with the data.

FIG. 6 shows an example of the geometrical relationships between a fieldof view of a user and objects. In this figure, the field of view 71 isdefined in the virtual three-dimensional space and information objects73 are arranged in the space. A fixed field-of-view coordinate system 72is defined relative to the field-of-view 71. Further, a viewpoint 70 isdefined at the location of the origin of the field-of-view coordinatesystem 72. The geometrical relationships of the objects relative to thefield-of-view can be defined, for example, with a transformation matrixfor transforming the local coordinate systems of the objects into thefield-of-view coordinate system 72.

At Step 404, in accordance with the viewpoint and the field of view, thecontroller 103 determines positions of the respective objects in thevirtual three-dimensional space in accordance with the respective objectdata sets 30 stored in the object data memory 113, and generatestwo-dimensional images of the respective objects and stores them in theRAM 122. For this purpose, when a required object data set has not beenstored yet in the object data memory 113, the controller 103 capturesthe required object data set into the object data memory 113 via thenetwork interface 127 or from the information storage device 107.

At Step 406, in accordance with the subroutine shown in FIG. 5, thecontroller 103 renders the generated images of the plurality of objectsshown as the example in FIG. 3 onto the two-dimensional frame memoryarea of the RAM 122, in accordance with the viewpoint and the field ofview.

In the flow chart shown in FIG. 4, all of the object images aregenerated at Step 404, and then the generated images are rendered atStep 406. However, Step 404 may be eliminated, and, at Step 406, theimages of the objects may be generated and stored in the RAM 122 in theorder of rendering, while the generated images may be retrievedsequentially from the RAM 122 for rendering.

At Step 408, the controller 103 determines whether the field of view hasbeen moved, i.e., whether the viewpoint and field of view data have beenupdated by the user. If the field of view has been moved, the procedurereturns to Step 402. Thus, Steps 402 through 406 are repeated while theviewpoint and the field of view keep moving. When the field of view hasnot been moved, the procedure advances to Step 412.

At Step 412, the controller 103 determines whether it has receiveduser's input data after a predetermined delay time (e.g., one second).If it has received the input data, the procedure advances to Step 414.When it has received no input data, the procedure returns to Step 412.Thus, the controller 103 waits for receipt of new input data.

At Step 414, the controller 103 determines whether the input datacorresponds to a termination command. If the input data corresponds tothe termination command, the procedure exits from the routine of FIG. 4.When it does not correspond to the termination command, the procedurereturns to Step 402.

Steps 402 through 414 are executed at a rate of thirty or more times persecond, to thereby generate sixty frames per second.

FIGS. 7A through 7C show an example of display screens of object imagesduring the zooming-in operation, in accordance with movement of theviewpoint.

As shown in FIG. 7A, objects of a box 611 having no lid, a sphere 613and a triangular cone 615 disposed on a rectangular object 601 arearranged in a virtual three-dimensional space. The rectangular object601 is linked to the box 611, the sphere 613 and the triangular cone615. As shown in FIG. 7C, the box 611 contains two spheres 621 and 622and one circular cylinder 623. The box 611 is linked to the two spheres621 and 622 and the circular cylinder 623.

As shown in FIGS. 7A through 7C, as the box 611 gets zoomed in, enlargedversions of the box 611 and the objects 621 to 623 within the box 611are displayed.

FIG. 5 shows a schematic flow chart of a subroutine for rendering theimages of the objects at Step 406 in FIG. 4 that is executed by thecontroller 103.

The flow chart in FIG. 5 is described below with reference to an exampleof rendering the images of the object 601 and the subsequent objects 611to 615 and 621 to 623 to be linked thereto in FIGS. 7A through 7C.

At Step 502, the controller 103 retrieves the image data set of astarting or current object from the RAM 122. This image data set hasbeen generated in accordance with the three-dimensional shape data (31in FIG. 2) contained in the object data set of the corresponding objectat Step 404 shown in FIG. 4, to store the generated image data set inthe RAM 122. In the example of FIG. 7A, the controller 103 retrievesfrom the RAM 122 the image data set of the rectangle 601 as the startingobject, which has been generated in accordance with thethree-dimensional shape data within the object data set 301 (FIG. 3) ofthe rectangle 601.

At Step 504, the controller 103 renders a front or visible side surfaceof one of one or more polygon surfaces of the current object that isdeepest or farthest from the viewpoint. In the example in FIG. 7A, thecontroller 103 renders a top or visible side surface of the rectangle601. A bottom side surface of the rectangle is located behind the topside surface and is not visible from the viewpoint.

At Step 506, the controller 103 puts into a queue all of the link datasets contained in the object data set of the current object, in order ofthe depth or farness from the viewpoint. In the example in FIG. 7A, thecontroller 103 puts the three link data sets 213, 211 and 212 for thesphere 613, the box 611 and the triangular cone 615, respectively, thatare contained in the object data set 301 of the rectangle 601, into aqueue in this order.

At Step 508, the controller 103 determines whether there is a remaininglink data set in the queue that indicates a link to another object whichhas not been rendered yet. If it determined that there is such aremaining link data set, the procedure advances to Step 510. If it isdetermined that there is no remaining link data set, the procedureadvances to Step 514. In the example in FIG. 7A, the procedure advancesto Step 510, since there remain in the queue the three link data sets213, 211 and 212 that indicate the links to the respective objects 613,611 and 615.

At Step 510, the controller 103 retrieves one of the remaining link datasets from the queue in the order. In the example in FIG. 7A, thecontroller 103 first retrieves the link data set 213 which indicates thelink to the sphere 613.

At Step 512, the controller 103 retrieves from the RAM 122 the imagedata set of the object to be, linked to in accordance with the retrievedlink data set, to thereby render an image of the object. For thispurpose, the controller 103 first renders a front side surface of afarther polygon surface of the object from the viewpoint, and thenrenders a front side surface of a closer polygon surface thereofrelative to the viewpoint. In the example in FIG. 7A, the controller 103renders only the outer side surface of the closer hemisphere of thesphere 613 that is closer to the viewpoint, because the inner sidesurface of a farther hemisphere of the sphere 613 is not visible.

In a similar manner, Steps 508 through 512 are repeated for the numberof times corresponding to the number of the remaining link data sets inthe queue, to thereby render the images of the remaining objects to belinked to the starting object. In the example in FIG. 7A, the images ofthe box 611 and the triangular cone 615 are rendered in the order.

At Step 514, the controller 103 renders the front side surface of one ofthe polygon surfaces of the starting object that is closer to theviewpoint. In the example in FIG. 7A, however, the controller 103 doesnot render a polygon surface of the rectangle 601 that is closer to theviewpoint, because it has no closer polygon surface.

In the manner described above, in accordance with the flow chart shownin FIG. 5, the images of the objects linked to the starting object arerendered after the rendering of the front side surface of the fartherpolygon surface of the starting object and before the rendering of thefront side surface of the closer polygon surface of the starting object.The starting object may have either a farther polygon surface or acloser polygon surface.

At Step 512, for rendering an image of one object which is linked toanother object, the controller 103 separately executes the subroutinefrom Steps 502 to 514, assuming the one object as a new starting object.Thus the subroutine at Step 512 is nested. Thus an image of the otherobject linked to the new starting object is rendered between the firstrendering of the front side surface of the farther polygon surface ofthe new starting object and the final rendering of the front sidesurface of the closer polygon surface of the new starting object.

In the example in FIG. 7A, when the controller 103 renders the image ofthe box 611 at Step 512, it separately executes Steps 502 through 514,assuming the box 611 as a starting object.

FIGS. 8A to 8E show an example of the process for rendering the imagesof the plurality of objects in accordance with the invention.

Referring to FIGS. 8A through 8E, the process for rendering the imagesof the box 611 as a starting object, the sphere 621, the circularcylinder 623 and the sphere 622 in accordance with the flow chart ofFIG. 5 is described below.

At Step 502, the controller 103 retrieves the image data set of the box611 from the RAM 122. This image data set has been generated inaccordance with the shape data in the object data set 311 in FIG. 3 andstored in the RAM 122, at Step 404 shown in FIG. 4. When Step 404 inFIG. 4 is eliminated as described above, the image of the box 611 isgenerated and stored in the RAM 122 at Step 502 before the rendering.

At Step 504, the controller 103 renders three inner side surfaces 6111,6112 and 6113 of three respective deeper polygon surfaces of the box611, as shown in FIG. 8A.

At Step 506, the controller 103 puts into a queue three link data sets221, 223 and 222 within the object data set 311 of the box 611 in thisorder that indicate respective links to the sphere 621, the circularcylinder 623 and the sphere 622, respectively.

At Step 508, the controller 103 first determines that there remain inthe queue the link data sets 221, 223 and 222 that indicate the links tothe respective objects which have not yet been rendered, and hence theprocedure advances to Step 510.

At Step 510, the controller 103 retrieves a first link data set 221 fromthe queue.

At Step 512, the controller 103 retrieves, from the RAM 122, the imagedata set of the sphere 621 which is linked by the link data set 221, andrenders the image of the sphere 621 as shown in FIG. 8B. The inner sidesurface of the farther hemisphere of the sphere 621 is not visible, andhence an outer side surface of only a hemisphere closer to the viewpointmay be rendered. After that the procedure returns to Step 508. When Step404 shown in FIG. 4 is eliminated as described above, the image of thesphere 621 is generated at Step 512 before the rendering.

Similarly, Steps 508 through 512 are reiteratively executed for thecircular cylinder 623 and the sphere 622, and the images of the circularcylinder 623 and the sphere 622 are rendered in the order as shown inFIGS. 8C and 8D.

At Step 514, the controller 103 renders outer side surfaces 6114 and6115 of closer ones of polygon surfaces of the box 611 as shown in FIG.8E. In this manner, the images of the box 611, and the sphere 621, thecircular cylinder 623 and the sphere 622 linked thereto are rendered.

It will be understood that execution of the flow chart in FIG. 5 resultsin sorting the objects in accordance with the hierarchy as shown in FIG.3.

In the flow chart in FIG. 5, the hierarchical sorting is performedsimultaneously with the rendering. Alternatively, the hierarchy as shownin FIG. 3 may be first determined, then the objects may be sorted inaccordance with the hierarchy into the order of the distance fromfarther to closer objects relative to the viewpoint, and then the imagesof the objects may be rendered in the sorting order. In this case, whena particular object is linked to another object in accordance with alink data set, the other object is rendered after the rendering of thefarther polygon surface of the particular object and before therendering of the closer polygon surface of the particular object.Alternatively, when a particular object having both of a farther polygonsurface and a closer polygon surface is linked to another object, thefarther polygon surface and the closer polygon surface may be sortedtogether with the other object and the order of rendering may bedetermined accordingly. If an object having a plurality of polygonsurfaces is linked to no subsequent object, generally it is not requiredto be separated into individual polygon surfaces for sorting.

Thus the images of subsequent objects to which one object is linked arerendered sequentially. For rendering an image of a current object linkedto be linked from, an image of a subsequent object to be linked theretois required to be rendered before or after the rendering of the image ofthe current object or in the course of the rendering. In other words,the images of the objects are locally depth-sorted in accordance withthe links between the objects.

FIG. 9A shows a displayed image in which the object 611 in FIG. 8E issemi-transparent. In FIG. 9A, the dotted lines indicate lines which canbe seen through. In this case, for rendering the polygon surfaces 6114and 6115 of the box 611, the colors of the polygon surfaces 6111 and6112 therebehind and of the outer side surface of the closer hemisphereof the sphere 622 are mixed with the color of the polygon surface 6114in overlapped portions thereof, while the colors of the polygon surfaces6111 and 6113 and of the outer side surface of the closer hemisphere ofthe sphere 622 are mixed with the color of the polygon surface 6115 inoverlapping portions thereof.

FIG. 9B shows a displayed image in which the objects 611, 621, 622 and623 in FIG. 9A are semi-transparent. For rendering the image of thesphere 621, the colors of the polygon surfaces 6111, 6112 and 6113therebehind are mixed with the color of the sphere 621 in overlappingportions thereof. For rendering the image of the circular cylinder 623,the images of the objects which lie behind the circular cylinder 623 andhave been rendered previously are mixed with the image of the circularcylinder 623 in overlapping portions thereof. For rendering the image ofthe sphere 622, the images of the objects which lie behind the sphere622 and have been rendered previously are mixed with the image of thesphere 622 in overlapping portions thereof. For rendering the polygonsurfaces 6114 and 6115, the images of the objects which lie behind thesepolygon surfaces and have been rendered previously are mixed with theimage of the sphere 622 in overlapping portions thereof.

By sorting the objects hierarchically as described above, the images ofthe objects are efficiently rendered. Thus not all polygon surfaces ofall objects may be required to be sorted. In the examples describedabove, however, complex arrangement is not shown such that two objectsintersect each other in a three-dimensional space. In such complexarrangement, each object may be divided into two object portions alongan intersecting polygon surface, and the object portions may be sortedhierarchically together with other objects.

The above-described embodiments are only typical examples, and theirmodifications and variations are apparent to those skilled in the art.It is apparent that those skilled in the art can make variousmodifications to the above-described embodiments without departing fromthe principle of the invention and the accompanying claims.

1. An information processing apparatus for displaying a plurality oflinked objects in a virtual three-dimensional space in accordance withfield-of-view data, said field-of-view data defining a field-of-view anda viewpoint in said virtual space, said information processing apparatuscomprising: a memory for storing object data; and control means forgenerating images of said objects in accordance with said object datastored in said memory and rendering said generated images onto atwo-dimensional frame, said control means rendering the image of oneobject and the image of a subsequent object to which said one object islinked, wherein the entire image of said subsequent object is renderedbetween a start and an end of rendering said one object, so that therendering of the entire image of said subsequent object is initiated andalso completed while the rendering of said one object is discontinued.2. The information processing apparatus according to claim 1, whereinsaid control means renders the image or partial images of said oneobject and the image of said subsequent object in accordance with thedistance from said viewpoint.
 3. A program storage medium readable by acomputer, tangibly embodying a program of instructions executable by thecomputer to perform a method for displaying a plurality of linkedobjects in a virtual three-dimensional space in accordance withfield-of-view data, said field-of-view data defining a field-of-view anda viewpoint in said virtual space, said method comprising the steps of:generating images of said objects in accordance with object data, saidobject data being stored in a memory, and rendering said generatedimages onto a two-dimensional frame, wherein the step of renderingcomprises a sub-step of rendering the image of one object and the imageof a subsequent object to which said one object is linked, wherein theentire image of said subsequent object is rendered between a start andan end of rendering said one object, so that the rendering of the entireimage of said subsequent object is initiated and also completed whilethe rendering of said one object is discontinued.
 4. The program storagemedium according to claim 3, wherein the step of rendering comprises asub-step of rendering the image or partial images of said one object andthe image of said subsequent object in accordance with the distance fromsaid viewpoint.
 5. A method for displaying a plurality of linked objectsin a virtual three-dimensional space in accordance with field-of-viewdata, said field-of-view data defining a field-of-view and a viewpointin said virtual space, said method being performed by a computer andcomprising the steps of: generating images of said objects in accordancewith object data, said object data being stored in a memory, andrendering said generated images onto a two-dimensional frame, whereinthe step of rendering comprises a sub-step of rendering the entire imageof one object and the image of a subsequent object to which said oneobject is linked, wherein the image of said subsequent object isrendered between a start and an end of rendering said one object, sothat the rendering of the entire image of said subsequent object isinitiated and also completed while the rendering of said one object isdiscontinued.
 6. The method according to claim 5, wherein the step ofrendering comprises a sub-step of rendering the image or partial imagesof said one object and the image of said subsequent object in accordancewith the distance from said viewpoint.
 7. An information processingapparatus for displaying a plurality of linked objects in a virtualthree-dimensional space in accordance with field-of-view data, saidfield-of-view data defining a field-of-view and a viewpoint in saidvirtual space, said information processing apparatus comprising; amemory for storing object data; and a control device generating imagesof said objects in accordance with said object data stored in saidmemory and rendering said generated images onto a two-dimensional frame,said control device rendering the image of one object and the image of asubsequent object to which said one object is linked, wherein the entireimage of said subsequent object is rendered between a start and an endof rendering said one object, so that the rendering of the entire imageof said subsequent object is initiated and also completed while therendering of said one object is discontinued.